Plug fuse



y 7, 1940. F. (1. LA MAR 2.199.835

PLUG FUSE Filed March 11, 1937 @(giij O 33 35 C T" R 3 P/flQ/ 24 illll INVENTOR 24 2 4. flaw BY g ATTORNE? Patented May 7, 1940 UNITED STATES PATENT OFFICE 2,199,835 PLUG FUSE I Frank G. La Mar, New York, N. Y.

Application March 11, 1937, Serial No. 130,271

'3 Claims.

This invention relates to an electric fuse of the plug type, especially to such a fuse having a casing of glass or like transparent, .not readily 1 .sirable characteristics of a fuse plug structure of the class described, may be mentioned the fol-- lowing:

(1) A reliable visible indication of the condition of the circuit to be protected should be provided at all times, both when the fusible element is intact, and when it has been blown;

(2) The flame consequent upon fusion should be confined, while the hot gases produced by fusion should be dissipated and vented at a sufliciently reduced temperature to prevent ignition thereby of nearby inflammable materials;

-(3) The cost of maintaining protection of the circuit should be kept as low as possible;

(a) By providing parts which can be used repeatedly;

(b) By reducing the initial cost of elements which when expended must be replaced by fresh parts; 7

(4) The operation ofreplacing expended parts should be of a simple character, accomplished readily by persons having no more technical knowledge, skill, nor experience than can be expected from members of the average household.

Inasmuch as known fuse plug structures do not respond satisfactorily to the above requirements in every respect, and some are lacking in more than one of the desired properties, it is the principal object of the present invention to provide a fuse plug structure which shall afford to an optimum extent the desired economy of structure and maintenance; the ease of replacement; and last, but not least, the provision for a reli able indication of circuit conditions at all necessary times, which are notably outstanding among the characteristics of a satisfactorily efficient fuse plug structure as above recited.

Another object of the invention is to assure a high factor of safety by providing for restraining flame and venting gases at a temperature which is innocuous.

Still another object is to provide a fuse car-' tridge which can be easily manipulated. T Another object is to provide a fuse plug structure in which the expendable fuse cartridge can be used, removed and replaced with only such aptitude as is required in use of the conventional 1 one-time fuse plugs known upon the'market.

Other objects and features of the invention will appear as the description of the particular physical embodiment selected to illustrate the inven-- tion progresses. T

In the accompanying drawing, like characters of reference have been applied to corresponding parts throughout the several views of the drawing, in which:

Figure l is a view in vertical section of an elec- I trical fuse-plug structure in the construction of which the present invention has been embodied;

Fig.- 2 is a view in plan thereof, partly broken away to reveal interior structure; Fig. 3 is a view in reverse plan looking from the bottom of the structure shown in Fig. 2 toward the top thereof, and also partly brokenaway; Fig. 4 is a detail view in perspective of the fuse cartridge mem ber illustrated in the preceding figureashown separately; Fig. 5 is a view in vertical sectional elevation of a modification; Fig. 6 is a similar view of another modification.

In a now-preferred embodiment of the invention selected for illustration and description, the reference character C designates generally a cas-: ing 1 member, and the reference character B designates generally a fuse cartridge including a' base for a fusible element F, which in accordance with the invention, is confined within the base B, and constitutes therewith a unitary structure 'inv sertable snugly within, and removable readily from, a cavity I I in the casing C.;

The base B may desirably be substantially bottle-shaped as shown, witha cavity l2 large enough to damp the flame from the fuse F when the latter is blown, the bottom of the bottle being provided with a central contact terminal T-, which may conveniently take the form of a tubular rivet the inner end of which is upset, as at. [4, and filled with a solder seal l5 by which agood mechanical and electricalconnection isxeifected so a with one end, of the fusible link or elementl;

which extends upwardly therefrom to the neck Hi of the bottle-shaped base B.

Across the mouth of the latter is disposed a. fusible portion I? of restricted dimensions (see Figs. 2 and 4), designed to localize the fusing, effect at a readily observableregion of the cartridge, and which in pursuance of the invention."

is arranged in parallel juxtaposition with the top l8 of the casing C, and can be viewed through a suitably transparent observation area thereof.

While provision for such visibility of the fusible construction I! while it remains intact, and of the gap left thereby when fused, can be most desirably effected by the use of an all glass casing member, as C, having a conventional flat top, or a top of slightly magnifying arcuate form, as at C in Fig. or C in Fig. 6, the desired visibility can be secured by the use of windows of known glazed or other suitableconstruction.

In pursuance of the invention, the top region of the casing designed for viewing the localized fusion station I! in the manner above described,

is furnished with a means to prevent access by flame from a blown fusible element F to the viewing top structure l8, so that the latter will not be cracked by heat nor fogged by the hot gases extended from the cavity |2 when a fusible element F is blown.

For the above protective purpose, a member 20 of suitably transparent, infusible and desirable refractory material such as a sheet of mica, is interposed between the top l8 of the casing C and the neck l6 of the bottle-shaped base B, completely overlying the mouth of the bottleshaped base and the constriction I! of the fusible element, but not interfering with desirable visibility thereof.

A convenient means for holding the protective mica disc 20 in place is illustrated in Figs. 1 to 4, taking the form of a cap 2| of metal, fitted retentively over the shoulder 22 of the bottle neck of the base B, in such fashion that the annular rim 23 of the cap (see Fig. 1) prevents any substantial displacement of the disc 20, but aifords a slight clearance for lateral escape of hot gases circumferentially into the upper cavity .|3 of the casing, causing the gases to be distributed radial-c ly in all directions, and thus dissipated and subjected to the cooling effect consequent upon their,

expansion from the cavity I2 to the radially larger cavity I3, and thence into the atmosphere,

"between the outer wall 24 of the bottle-shaped base B and the inner wall 25 of the casing C'.

This cylindrical clearance affords a natural vent which may be relied upon to relieve any serious strain upon the walls of the glass casing 20, and as the evidence of the complete dissipa- X protected, the base B is shown as formed with a lengthwise extending outer groove 28 adapted to receive the inner shank 29 of a flat spring of which the terminal T is formed, the other shank 30 of the spring lying within a groove 3| in the periphery of the casing C, where it is confined by the shell-S, being united to the latter mechanically and electrically, as by solder, at 32.

The inner free end of the contact element T" is formed as a ring 33 which is so presented within the upper confines |3 of the cavity II that when the fuse-cartridge is pushed into the casing, which can only be accomplished when. the groove 28 is in alignment with the spring 29, the nose 34 of the cap 2| (see Fig. 4), will contact first with the free end 35 of the ring 33 and ultimately the entire annular under face of the ring will be brought into rubbing contact with the entire upper annular face of the ring cap 2|.

The central orifice of the ring 33 on contact terminal T" is in alignment with the central orifice of the cap 2|, and these orifices define an observation opening unobstructed visually by the mica window 20 and by the transparent top l8 of the glass casing C, although no fused metal can reach the glass l8 through the mica shield 20.

As long as the constriction I1 is intact it can be seen clearly; and when fused, that event is made evident, either by absence of the part I! or by a fog of spattered metal on the disc 20. Visibility can be aided by forming the top l8 of the casing C with a suitable contour to afford a lenticular structure, as by an all-over arcuate shape shown at C in Fig. 5, or by a local arcuate central enlargement, as at C" in Fig. 6 which are illustrative of means for producing a desirable magnification.

The flame and hot metal are thus retained within the bottle B, and the residuum will be removed when this bottle-shaped fuse cartridge is pulled out and discarded preparatory to its replacement by a fresh fuse cartridge in the manner already described.

The hot gases, as already noted, will escape harmlessly, first around the loose disc 20 and central orifices of the rings 34 and 35, and secondly between the cap 2| and bottle neck Hi, the cap 2| being held away somewhat from the outer face of the neck l6 by the end 36 of the fusible element F, which is metallically united to the inner face of the cap as indicated in Figs. 1 and 4.

The groove 28, added to the clearance between the bottle and casing, yields an ample avenue for venting the gases in completely spent condition.

The flange 31 at the free end of the shell S aids to protect the free end of the glass casing C, but does not interfere with ready insertion and withdrawal of the fuse cartridge B, which projects sufliciently to facilitate manipulation thereof digitally.

From the foregoing, it will be seen readily that any of a series of spare fuse cartridges B can be used interchangeably in any of a series of casings C, and each casing C will outlive many of the fuse-cartridges as expended in use.

Accordingly, the invention provides for a marked decrease in the initial cost, and inexpensive maintenance of protection of electrical circuits by devices in the construction of which the present invention has been embodied; also providing for improved security and for greater convenience in use.

Although I have particularly described one particular physical embodiment of my invention and explained the operation, construction and principle thereof, nevertheless, I desire to have it understood that the form selected is merely illustrative, but does not exhaust the possible physical embodiments of the idea of means underlying my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. A fuse plug structure having a casing member made of insulating material with a top portion through which the interior of the casing is readily observable, said casing being threaded externally and fitted with a metal contact-terminal shell having complemental threads; and said casing being provided with a contact-terminal member such as a strap leading to the interior of said casing and having its inner end disposed adjacent to the observation portion, being formed into a contact-terminal ring having a central view orifice; a fuse-cartridge member comprising a substantially bottle-shapedbase of insulating, flame-resistant structure adapted to slide snugly into and out of said casing, and having a longitudinal peripheral groove adapted to receive said strap terminal and to be held thereby in predetermined position both positively against rotation within the casing and frictionally against coaxial movement relatively thereto, said base being of suitable length to extend out of said casing, and having a substantially conventional central contact-terminal for engagement with a socket terminal, a fusible element making good mechanical and electrical connection with said central contact-terminal, and having a preponderant portion of its length confined within the cavity of the base, and a ringshaped terminal connected with said fusible element and adapted to be presented at the mouth of the bottle for making removable contact with the complemental terminal ring adjacent to the observation portion of the casing; said fusible element being further characterized by having a portion of reduced cross-section disposed across the bottle mouth in alignment with the orifices of said rings and readily observable through the top of said casing, and a window patch or element of transparent, non-inflammable material interposed between said base and easing, serving to prevent access of hot gases directly to the top of said casing when a fusible element blows, said base and easing being of such contour at their interfitted parts as to permit restricted escape of said gases therebetween, While flame is confined within the cavity of said bottle.

2. As a new article of manufacture, a structural member for a fuse plug of the class described; said member comprising a hollow one-piece glass casing having a body cavity, substantially cylindrical walls exteriorly threaded and having a groove intersecting the convolutions of said threads; a threaded contact terminal shell fitted upon said exterior threads, whereby said plug is adapted to be screwed into a fuse block; and a U-shaped metal connector straphaving a good mechanical and electrical connection with said shell and having one shank disposed in said groove, the other shank extending within said cavity and terminating in a ring-shaped contact terminal extended across the top region of the cavity, being biased yieldingly away from the top of the casing by its inherent resiliency; said casing-member constituting an entity adapted to be used an indefinite number of times by being interfitted in complemental relation with any suitable cartridge fuse member of a series suitable for such use, said cartridge fuse member being formed with a longitudinal peripheral groove in which said connector strap lies whereby the connector strap prevents unscrewing of the external shell of the casing and also prevents rotatlon of the fuse cartridge within the cavity of the casing.

3. A fuse plug structure having a casing member made of insulating material with a top portion through which the interior of the casing is readily observable, said casing being threaded externally and fitted with a metal contact-terminal shell having complemental threads; and said casing being provided with a contact-terminal member such as astrap leading to the interior of said casing and having its inner end disposed adjacent to the observation portion, being formed into a contact-terminal ring having a central view orifice; a fuse-cartridge member comprising a substantially bottle-shaped base of insulating, flameresistant structure adapted to slide snugly into and out of said casing, and having a longitudinal peripheral groove adapted to receive said strap terminal and to, be held thereby in predetermined position both positively against rotation within the casing and frictionally against coaxial movement relatively thereto.

FRANK C. LA MAR. 

